Compiler Construction

Transcription

1 Drawing Hands M.C. Escher, 1948 Staff: Compiler Construction Viktor Kuncak Lectures Etienne Kneuss Labs Eva Darulova Exercises Yvette Gallay secretary

2 Example: javac - from Java to Bytecode while (i < 10) { System.out.println(j); i = i + 1; j = j + 2*i+1; } javac Test.java Test.class javap c Test 4: iload_1 5: bipush 10 7: if_icmpge 32 10: getstatic #2; //System.out 13: iload_2 14: invokevirtual #3; //println 17: iload_1 18: iconst_1 19: iadd 20: istore_1 21: iload_2 22: iconst_2 23: iload_1 24: imul 25: iadd 26: iconst_1 27: iadd 28: istore_2 29: goto 4 32: return You will build a compiler that generates such code

3 Example: gcc - from C to Intel x86 #include <stdio.h> int main(void) { int i = 0; int j = 0; while (i < 10) { printf("%d\n", j); i = i + 1; j = j + 2*i+1; } } gcc test.c S test.s.l3:.l2: jmp.l2 movl -8(%ebp), %eax movl %eax, 4(%esp) movl $.LC0, (%esp) call printf addl $1, -12(%ebp) movl -12(%ebp), %eax addl %eax, %eax addl -8(%ebp), %eax addl $1, %eax movl %eax, -8(%ebp) cmpl $9, -12(%ebp) jle.l3

4 i = 0 LF w h i l e i=0 while (i < 10) { a[i] = 7*i+3 i = i + 1 } lexer i = 0 while ( i < 10 ) source code (e.g. Scala, Java,C) easy to write Compiler (scalac, gcc) parser type check assign while characters words trees i 0 assign + a[i] * 7 i machine code (e.g. x86, ARM, JVM) efficient to execute < i 10 3 mov R1,#0 mov R2,#40 mov R3,#3 jmp +12 mov (a+r1),r3 add R1, R1, #4 add R3, R3, #7 cmp R1, R2 blt -16 Compiler Construction data-flow graphs optimizer code gen

5 Compilers are Important Source code (e.g. Scala, Java, C, C++, Python) designed to be easy for programmers to use should correspond to way programmers think help them be productive: avoid errors, write at a higher level, use abstractions, interfaces Target code (e.g. x86, arm, JVM,.NET) designed to efficiently run on hardware / VM fast, low-power, compact, low-level Compilers bridge these two worlds, they are essential for building complex software

6 A pioneering compiler: FORTRAN (FORmula TRANslator) Backus-Naur Form - BNF Turing Award 1977

7 Challenges for Future Can target code commands include not only execution of commands on standard microprocessors processors, but also automatic design of new hardware devices, and control of physical devices? Can compilers bridge the gap between wishes and commands, and help humans make the right decisions? Can source code programs be wishes: specification languages, math, natural language phrases, diagrams, other forms of communication closer to engineers and users?

8 Some of Topics You Learn in Course Develop a compiler for a Java-like language Write a compiler from start to end Generates Java Virtual Machine (JVM) code (We provide you code stubs, libraries in Scala) Compiler generators using and making them Analyze complex text Automata, regular expressions, grammars, parsing Automatically detecting errors in code name resolution, type checking, data-flow analysis Machine-like code generation

9 Potential Uses of Knowledge Gained understand how compilers work, use them better gain experience with building complex software build compiler for your next great language extend language with a new construct you need adapt existing compiler to new target platform (e.g. embedded CPU or graphics processor) regular expression handling in editors, grep build an XML parsing library process complex input box in an application (e.g. expression evaluator) parse simple natural language fragments

10 Schedule and Activities (6 credits) All activities take place in INM 202 Mondays 10:15-12:00, Wednesday 8:15-10:00 and continuing to: Wednesday 10:15-12:00 Lectures, Labs, Exercises At home Continue with programming the compiler Write the homework If you need more help, us: we will arrange additional meetings

11 How We Compute Your Grade 55% : project (submit, explain if requested) submit through our wonderful online system do them in groups of 2, exceptionally 1 or 3 20% : homework in the first part of the course do them individually! submit at the beginning of next exercise participate in exercise sessions 25% : quiz in the last week of classes will be on the last Wednesday of classes do it individually Must get > 60% from each category to get 4.0

12 Collaboration and Its Boundaries For clarification questions, discuss them in the mailing list, which we monitor Work in groups of 2 for project everyone should know every part of code we may ask you to explain specific parts of code Do not copy lab solutions from other groups! we use code plagiarism detection tools we will check if you fully understand your code Do the homework and quiz individually You wouldn t steal a handbag. You wouldn t steal a car. You wouldn t steal a compiler or homework!

13 i=0 while (i < 10) { a[i] = 7*i+3 i = i + 1 } source code simplified Java-like language Your Compiler Construction i = 0 LF w h i l e lexer i = 0 while ( i < 10 ) Your Compiler parser type check assign while characters words trees Each two weeks you will add next phase - keep same groups i 0 assign + a[i] * 7 i - it is essential to not get behind schedule - final addition to compiler is your choice! JVM Code < i : iload_2 22: iconst_2 23: iload_1 24: imul 25: iadd 26: iconst_1 27: iadd 28: istore_2 code gen

14 EPFL Course Dependencies Theoretical Computer Science (CS-251) If have not taken it, check the book Introduction to the Theory of Computation by Michael Sipser Knowledge of the Scala language (see web) Helpful general background Discrete structures (CS-150), Algorithms (CS-250) This course provides background for MSc: Advanced Compilers Synthesis Analysis & Verification Foundations of Software

15 Official Textbook: Course Materials Andrew W. Appel, Jens Palsberg: Modern Compiler Implementation in Java (2nd Edition). Cambridge University Press, 2002 We do not strictly follow it program in Scala instead of Java use pattern matching instead of visitors hand-written parsers in the project (instead of using a parser generator) Lectures in course wiki:

16 Additional Materials Compilers: Principles, Techniques, and Tools (2nd Edition) by Alfred V. Aho, Monica S. Lam, Ravi Sethi, Jeffrey D. Ullman comprehensive Compiler Construction by Niklaus Wirth concise, has main ideas Niklaus Emil Wirth (born February 15, 1934) is a Swiss computer scientist, best known for designing several programming languages, including Pascal, and for pioneering several classic topics in software engineering. In 1984 he won the Turing Award for developing a sequence of innovative computer languages. Additional recent books ( ): Aarne Ranta: Implementing Programming Languages H.Seidl, R.Wilhelm, S.Haack: Compiler Design (3 vols, Springer)

17 Describing the Syntax of Languages

18 Syntax (from Wikipedia)...In linguistics, syntax (from Ancient Greek σύνταξις "arrangement" from σύν - syn, "together", and τάξις - táxis, "an ordering") is the study of the principles and rules for constructing phrases and sentences in natural languages....in computer science, the syntax of a programming language is the set of rules that define the combinations of symbols that are considered to be correctly structured programs in that language.

19 Describing Syntax: Why Goal: document precisely (a superset of) meaningful programs (for users, implementors) Programs outside the superset: meaningless We say programs inside make syntactic sense (They may still be wrong in a deeper sense) Describing syntactically valid programs There exist arbitrarily long valid programs, we cannot list all of them explicitly! Informal English descriptions are imprecise, cannot use them as language reference

20 Describing Syntax: How Use theory of formal languages (from TCS) regular expressions & finite automata context-free grammars We can use such precise descriptions to document what each compiler should support manually derive compiler phases (lexer, parser) automatically construct these phases using compiler generating tools We illustrate this through an example

21 While Language Idea Small language used to illustrate key concepts Also used in your first lab interpreter later labs will use a more complex language we continue to use while in lectures while and if are the control statements no procedures, no exceptions the only variables are of int type no variable declarations, they are initially zero no objects, pointers, arrays

22 While Language Example Programs while (i < 100) { j = i + 1; while (j < 100) { println(,i); println(,,j); j = j + 1; } i = i + 1; } Nested loop x = 13; while (x > 1) { println("x=", x); if (x % 2 == 0) { x = x / 2; } else { x = 3 * x + 1; } } Does the program terminate for every initial value of x? (Collatz conjecture - open) Even though it is simple, while is Turing-complete.

23 Reasons for Unbounded Program Length constants of any length variable names of any length String constants of any length (words - tokens) nesting of expressions while (i < 100) { j = i + 5*(j + 2*(k + 7*(j+k) + i)); while ( > j) { while (k < 100) { somename42a = somename42a + k; k = k + i + j; println( Nice number, k) } } } nesting of statements

24 Tokens (Words) of the While Language Ident ::= letter (letter digit)* integerconst ::= digit digit* stringconst ::= AnySymbolExceptQuote* keywords if else while println special symbols ( ) && < == + - * / %! - { } ;, letter ::= a b c z A B C Z digit ::= regular expressions

25 Double Floating Point Constants Different rules in different languages 1) digit digit* [. ] [ digit digit* ] 2) digit digit* [. digit digit * ] 3) digit*. digit digit* 4) digit digit*. digit digit*

26 Identifiers while (i < 100) { j = i + 5*(j + 2*(k + 7*(j+k) + i)); while ( > j) { while (k < 100) { somename42a = somename42a + k; k = k + i + j; println( Nice number, k) } } } letter (letter digit)*

27 Id3 = 0 while (id3 < 10) { println(,id3); id3 = id3 + 1 } source code Compiler Construction i d 3 = 0 LF w lexer id3 = 0 while ( id3 < 10 ) parser assign i 0 while assign + a[i] * 7 i < i 10 3 characters words (tokens) trees Lexer is specified using regular expressions. Groups characters into tokens and classifies them into token classes.

28 More Reasons for Unbounded Length constants of any length variable names of any length String constants of any length (words - tokens) nesting of expressions while (i < 100) { j = i + 5*(j + 2*(k + 7*(j+k) + i)); while ( > j) { while (k < 100) { somename42a = somename42a + k; k = k + i + j; println( Nice number, k) } } } nesting of statements (sentences)

29 Sentences of the While Language We describe sentences using context-free grammar (Backus-Naur form). Terminal symbols are tokens (words) program ::= statmt* statmt ::= println( stringconst, ident ) ident = expr if ( expr ) statmt (else statmt)? while ( expr ) statmt { statmt* } expr ::= intliteral ident expr (&& < == + - * / % ) expr! expr - expr nesting of statements nesting of expressions

30 While Language without Nested Loops statmt ::= println( stringconst, ident ) ident = expr if ( expr ) statmt (else statmt)? while ( expr ) statmtww { statmt* } statmtww ::= println( stringconst, ident ) ident = expr if ( expr ) statmtww (else statmtww)? { statmtww* }

31 Id3 = 0 while (id3 < 10) { println(,id3); id3 = id3 + 1 } source code Compiler Construction i d 3 = 0 LF w lexer id3 = 0 while ( id3 < 10 ) parser assign i 0 while assign + a[i] * 7 i < i 10 3 characters words (tokens) trees regular expressions for tokens context-free grammar

32 Abstract Syntax - Trees To get abstract syntax (trees, cases classes), start from context-free grammar for tokens, then remove punctuation characters interpret rules as tree descriptions, not string descriptions statmt ::= println( stringconst, ident ) concrete syntax Scala trees for this abstract syntax PRINT(String,ident) ident = expr ASSIGN(ident,expr) if ( expr ) statmt (else statmt)? IF(expr,stmt,Option[statmt]) while ( expr ) statmt WHILE(expr,statmt) { statmt* } BLOCK(List[statmt]) abstract syntax abstract class statmt case class PRINT(id:ident) extends statmt case class ASSIGN(id:ident, e:expr) extends statmt case class IF(e:expr, s1:statmt, s2:statmt) extends statmt...

33 Example of Parsing res = 14 + arg * 3 Lexer: res = 14 + arg * 3 Parser: ASSIGN(res, PLUS(CONST(14), TIMES(VAR(arg),CONST(3)))) res := + 14 * arg 3 Code generator then prints this tree into instructions.

34 Reminder about Formal Languages

35 Languages Formally A word is a finite, possibly empty, sequence of elements from some set Σ Σ alphabet, Σ * - set of all words over Σ For lexer: characters; for parser: token classes uv denotes concatenation of words u and v By a language we mean a subset of Σ * union, intersection, complement wrt. Σ * L 1 L 2 = { u 1 u 2 u 1 in L 1, u 2 in L 2 } L 0 = ε L k+1 = L L k L * = U k L k (Kleene star)

36 Are there finitely many tokens? There are finitely many token classes identifier string { } (... (many, but finitely many) There is unbounded number of instances of token classes identifier and string When we discuss grammars, we work with token classes.

37 Σ = {a,b} Examples of Languages Σ * = {ε, a, b, aa, ab, ba, bb, aaa, aab, aba,... } Examples of two languages, subsets of Σ * : L 1 = {a, bb, ab} (finite language, three words) L 2 = {ab, abab, ababab,... } = { (ab) n n 0 } (infinite language)

38 Examples of Operations L = {a,ab} L L = { aa, aab, aba, abab } L* = { a, ab, aa, aab, aba, abab, aaa,... } (is bb inside L*?) = { w immediately before each b there is a }